EP0929743A1

EP0929743A1 - Radial piston pump

Info

Publication number: EP0929743A1
Application number: EP97939965A
Authority: EP
Inventors: Egon Eisenbacher
Original assignee: Mannesmann Rexroth AG
Current assignee: Hilite Germany GmbH
Priority date: 1996-10-01
Filing date: 1997-08-19
Publication date: 1999-07-21
Anticipated expiration: 2017-08-19
Also published as: DE19640596A1; EP0929743B1; DE59708963D1; ES2184129T3; WO1998014704A1

Abstract

Disclosed is a radial piston pump wherein the fluid to be compressed is drawn through the piston, which can be driven by an eccentric shaft. Piston inlet opening axis is displaced in relation to a centre plane of the drive shaft, parallel to the pistonaxis, so that one of the circumferential edges of the eccentric can be used to control the suction opening.

Description

description

Radial piston pump

The invention relates to a radial piston pump according to the preamble of patent claim 1.

In pumps of this type, a large number of cylinders are generally arranged in a star shape in one or more planes around a drive shaft, which is designed as an eccentric shaft. The pistons of the cylinders rest on the eccentric and make a constant stroke that corresponds to twice the eccentricity.

Such pumps are usually with pressure valves

- For example automatic, spring-loaded valves

- Equipped with which the pressurized medium can be ejected. The suction can take place via also automatically spring-loaded suction valves, which open during the suction stroke of the piston.

EP 0 520 286 B1 describes a radial piston pump in which an eccentric ring is mounted on the drive shaft, on the outer circumference of which flats are provided, against which the radial pistons rest. The rotary movement of the eccentric causes the eccentric ring to wobble, the pistons being moved in the radial direction and, in addition, a movement component parallel to the contact surface, i.e. in the tangential direction.

Instead of the suction valves described above, in the known radial piston pump, the pistons are provided with bores which open with an inlet opening in the end face of the piston. A tangential groove is formed in each flattened portion, which is at predetermined rotational positions due to the tangential displacement of the eccentric ring releases the inlet openings so that the fluid to be delivered can be sucked through the tangential groove and the bore of the piston.

Since the contact surface of each piston is reduced by the tangential grooves in the eccentric ring, relatively high surface pressures occur in such solutions, so that it is necessary to produce the eccentric ring from a comparatively hard material in order to avoid damage to the radial piston pump due to premature wear.

In contrast, the invention is based on the object of creating a radial piston pump in which wear can be reduced with minimal expenditure on device technology.

This object is achieved by the features of patent claim 1.

By taking the measure to open the inlet opening of the bore through the circumferential edge of the support surface lying in the direction of rotation - referred to below as the tangential surface - of the eccentric, a groove no longer needs to be formed in the tangential surface in order to open the inlet opening. By eliminating the grooves, which have to be manufactured with high precision, the manufacturing costs can be reduced to a minimum compared to the conventional solution. It is particularly preferred if an eccentric ring is provided between the eccentric and the piston, which is slidably guided on the drive shaft. The flat support of the piston end face enables the use of a material with emergency running properties for the eccentric ring, whereby the piston pressure due to the lower surface pressure The end face is partially relieved hydrostatically, so that premature wear of the eccentric ring can be largely avoided.

In principle, two solutions are available in order to be able to optimally open the inlet opening through the peripheral edge of the tangential surface.

In a first alternative, the piston bore axis, which in the conventional solutions was arranged coaxially to the central axes of the drive shaft cross section, is offset against the direction of rotation, so that the bore axis runs parallel to the corresponding central axis.

In a kinematic reversal of the above-mentioned principle, the tangential surface with respect to the piston axis can also be displaced in the direction of rotation, so that the same effect can be achieved.

The relative position of the circumferential edge opening the inlet opening with respect to the inlet opening can be varied in a simple manner by the dimension of the lateral offset between the piston end face and the tangential surface, so that the opening duration during the suction stroke can be adapted to different conditions.

The lateral displacement of the piston with respect to the tangential surface reduces the transverse forces acting on the piston during the working stroke compared to the conventional solution, so that less demands are made on the lateral support of the piston in the associated cylinder.

It is particularly advantageous if the inlet opening is designed with a rectangular cross section, so that a maximum suction cross-section is provided at the start of opening.

The inflow of the fluid to be conveyed can be further simplified if the tangential surfaces are each formed by a radial projection, so that the fluid can enter the opening cross section unhindered.

In the radial piston pump according to the invention, it is preferred if sealing devices are provided on the piston end face, so that an optimal sealing of the inlet opening is possible during the working stroke.

In particular, in the embodiment with a rectangular inlet opening, it is necessary to assign a rotation lock to the radial piston, so that the relative position between the opening peripheral edge of the tangential surface and the adjacent peripheral edges of the inlet opening is retained.

The lateral offset between the shaft cross-sectional axis and the bore axis can also be adjusted by forming the axis of the inlet opening at a distance from the piston axis.

A particularly uniform load on the eccentric ring and thus on the drive shafts is obtained if three cylinders, each with a working piston, are evenly distributed in one or more planes in the radial direction on the outer circumference of the drive shaft.

Tilting of the eccentric ring can be prevented if the working stroke of the piston is limited to a maximum, so that a flat contact of the piston end face with the tangential surface is always guaranteed. Other advantageous developments of the invention are the subject of the further subclaims.

Preferred exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings. Show it:

FIG. 1 shows a cross section through a first exemplary embodiment of a radial piston pump;

Figure 2 is a section along the line A-A in Figure i;

FIG. 3 shows a cross section through a further exemplary embodiment of a radial piston pump according to the invention;

FIG. 4 shows a detailed illustration of a piston end face and a tangential surface of an eccentric ring of a further exemplary embodiment of a radial piston pump according to the invention;

FIG. 5 shows a detailed illustration of a piston provided with a control chamfer and

Figure 6 is a detailed representation of a piston end face with seal and an eccentric ring of a last embodiment of a radial piston pump according to the invention.

Figure 1 shows a cross section of a radial piston pump 1 according to the invention, in which three circumferentially distributed pump cylinders 4 are arranged in a cylindrical or cup-shaped housing 2, the pistons 6 of which are driven by a pump drive shaft 8, the Stroke axes of the respective pistons 6 are arranged approximately in the radial direction of the drive shaft 8.

The housing 2 has a mounting flange, which is shown in section in FIG. 1 and on which through holes 10 for flange screws (not shown) are formed, which are distributed over a pitch circle, so that an end cover can be attached. A plurality of threaded bores 14 are formed in a rear wall 12 of the housing, by means of which the pump can be fastened to an assembly.

The axis of rotation 16 of the pump drive shaft 8 runs coaxially to the central axis of the housing, only one eccentric 18 being shown in the illustration according to FIG. 1, the drive shaft 8 extending perpendicular to the plane of the drawing. The eccentric axis is provided with the reference number 20 in FIG. The dimension of the eccentricity e corresponds - as already mentioned at the beginning - to half the stroke height of the piston 6.

The radial piston pump 1 has, coaxially to the drive shaft axis 16 and to the housing 2, an inner housing 22 which is provided with three cylinder receptacles 24 which extend in the radial direction and into which the cylinders 4 are screwed. The axial length of the cylinder receptacles 24 and the cylinders 4 is selected such that the end section of each cylinder 4 pointing toward the drive shaft 8 in FIG. 1 extends approximately tangentially to the cylindrical interior 26 of the inner housing 22. Each cylinder 4 is provided with a stop collar 28 with which the cylinder 4 is supported on the outer end face of the cylinder receptacle 24. A cylinder head 30 adjoins the stop collar 28 in the direction of the wall of the housing 2, in which a valve device 32 is received, via which a cylinder bore is directed outwards, that is to say from Housing 2, on the one hand, and the annular space 34 enclosed by the inner housing 22, on the other hand, can be shut off.

Figure 2 shows a section along the line A-A in Figure 1, wherein one of the cylinders 4 with the corresponding part of the eccentric 18 is shown in an enlarged view. Accordingly, the valve device 32 acts on a valve body 36, which is biased against a valve seat 40 in the cylinder head 30 via a spring 38. The valve body 36 bears against the outer end face of the cylinder head 30, so that the valve device 32 allows fluid flow out of the cylinder space, but prevents backflow.

Of course, instead of the check valve shown in FIGS. 1 and 2, other valve constructions, such as diaphragm valves, etc., can also be used.

A spring 44 is supported on an inner end face 42 of the cylinder head 30, via which the piston 6 is biased in the direction of the eccentric 18.

The cylinder bore is widened stepwise in the radial direction following the valve seat 36, the inner end face 42 being formed by a first step section. This first step-shaped section is then followed by the cylinder sleeve 46, which is expanded in the radial direction and in which the piston 6 is slidably received.

The piston 6 has an approximately cup-shaped cross section, an inlet opening 48 being formed in the bottom of the piston. The piston spring 44 acts on the inner end face of the piston 6 formed by the base in order to pretension the piston 6. The end section on the drive shaft side is designed as a diameter-reduced radial projection 50, the end face of which forms the contact surface of the piston 6.

In the exemplary embodiment shown, the end face of the piston 6 does not lie directly on the outer circumference of the eccentric 18 of the drive shaft 8, but an eccentric ring 52 with an inner bore 54 is formed between the eccentric 18 and the projection 50, which is passed through by the eccentric 18.

On the outer circumference of the eccentric ring 52, three flats 56 distributed over the circumference are formed (see FIG. 1), which serve as support surfaces for the pistons 6, which are supported with their end faces on the flats 56 by the spring preload.

As can be seen in particular from the representation of the cylinder 4 arranged in the vertical position at the top in FIG. 1, the piston axis 60 in the top dead center position of this piston 6 shown in FIG. 1 is by the measure opposite the central plane of the drive shaft 16 containing a perpendicular to the flattened portion 56 a offset against the direction of rotation Z (see arrow in Figure 1).

Furthermore, the width B of the flattening and the clear width o of the inlet opening 48 are selected such that the right peripheral edge running perpendicular to the plane of the drawing in FIG. 1 runs just outside the inlet opening 48. Since the inlet opening 48 during the further rotation of the eccentric 18 through this peripheral edge is opened, this is referred to below as a suction control edge 62.

Since the eccentric ring 52 slidably rests on the eccentric 18, the eccentric 18 does not follow the rotational movement of the eccentric 18, but is set in a wobble movement by this, this wobble movement a movement component in the stroke direction and a movement component parallel to the flattening, i.e. in the tangential direction. Accordingly, when the eccentric 18 rotates in the direction of the arrow Z in FIG. 1, the flattened portion 56 (top in FIG. 1) is moved radially inward and tangentially to the left (view according to FIG. 1) due to the eccentricity e, so that the piston 6 is shown 1 is moved downward and the suction control edge 62 opens the inlet opening 48. The fluid located in the interior 26 of the inner housing 22 can then flow into the interior of the piston through the inlet opening 48. The fluid is supplied from a tank to the interior 26 through a supply line, not shown.

The piston shown at the bottom right in FIG. 1 is currently in this suction position, in which the fluid is sucked into the interior of the piston. Due to the negative pressure in the cylinder space and the spring preload, the valve device 32 is closed, so that the sucked-in fluid cannot escape through the cylinder head 30.

The suction stroke of the piston 6 located at the top in FIG. 1 is ended when the drive shaft 6 - starting from the reference position shown - has rotated by 180 °, so that the eccentric center point is located vertically below the center point of the drive shaft, so that the suction stroke correspondingly doubles the eccentricity is e. In this rotational position of the drive shaft the suction control edge 62 is moved back into its starting position due to the wobbling movement of the eccentric ring 52, so that the inlet opening 48 is just closed and no more fluid can be sucked in.

As a result, i.e. When the drive shaft 8 is rotated further towards the starting position shown in FIG. 1, the piston 6 is moved upward again (working stroke), the suction control edge 62 always being arranged outside the inlet opening 48, so that it remains closed (see the one in FIG 1 piston 6) arranged at the bottom left. The piston 6 now carries out its working stroke, in which the pressurized fluid is expelled through the opening valve device 32 into the annular space 34 until the piston 6 has reached its top dead center shown in FIG. 1. The pressurized fluid in the annular space 34 is delivered to the consumer via a housing bore, not shown.

The other two pistons (bottom in FIG. 1) pass through corresponding suction / working cycles, these being offset from those of the piston 6 shown in FIG. 1, so that a quasi-continuous flow can be achieved.

In the embodiment shown in Figure 1, the lateral displacement (a) of the piston 6 with respect to the drive shaft plane is achieved by the receiving bore of the cylinder receptacle 24 is formed eccentrically, so that the cylinder receptacle 24 in the illustration of Figure 1 on the left side has a greater wall thickness than on the right side. Of course, the lateral displacement could also be effected by arranging the cylinder receptacle 24 accordingly, so that the receptacle bore would then be made centrally can. The length of the suction and working stroke can be determined by the choice of the overlap a, a 180 ° suction stroke being sought for an optimal filling of the piston.

Compared to conventional solutions of throttled radial piston pumps with suction openings in the piston skirt, the solution according to the invention has the further advantage that there is no loss of stroke volume.

Since the piston 6 is arranged with approximately h eccentricity offset from the shaft axis, the transverse forces acting on the piston 6 are reduced to a minimum during the working stroke.

A particularly good and quick filling of the piston and cylinder interior can be achieved if the inlet opening 48 is designed with a rectangular cross-section, one side edge being arranged parallel to the suction control edge 62, so that a large suction cross-section is available at the beginning of the control process is provided. In this variant, however, an anti-rotation device (not shown) must be assigned to the piston 6.

In the exemplary embodiment shown, the eccentric ring 52 is made of a material with emergency running properties, such as bronze, whereby wear compensation can take place due to the self-adjustment (spring preload of the piston 6 towards the support surface (flattening 56)). This choice of material also makes it possible to mount the eccentric ring 52 directly on the eccentric 18 of the drive shaft 8 without a bearing bush having to be provided. Instead of the lateral displacement of the piston with respect to the drive shaft plane, the inlet opening 48 can also be made eccentrically in the piston head, so that the same effect occurs (anti-rotation required).

The exemplary embodiment shown in FIG. 3 differs from the previously described exemplary embodiment only in the configuration of the eccentric ring 52, so that the other components are not described again.

The eccentric ring 152 of the exemplary embodiment shown in FIG. 3 is not designed in the form of a ring with flattened portions, but with three radial projections 64 which protrude from the ring circumferential surface 66 in the radial direction. That is, in the exemplary embodiment shown in FIG. 3, the side areas marked with X and delimiting the flats 56 are cut free, so that when the inlet opening 48 is opened, the inflow of the fluid into the piston 6 is facilitated, so that the pressure losses in the pump are reduced Minimum can be reduced and thus the efficiency is increased. Furthermore, in this exemplary embodiment, the material expenditure for producing the eccentric ring 152 is reduced to a minimum, since the ring walls in the area of the ring peripheral surfaces 66 are reduced to a minimum.

In order to prevent the eccentric ring 152 from tilting with respect to the piston 6, the axial lengths of the cylinder 4 and the piston 6 and the radial spacing of the flat 56 with respect to the eccentric axis 20 are selected such that the piston 6 strikes the cylinder head 30 before the eccentric ring is out can tilt out of its contact position, so that tilting without damaging the eccentric ring 152 is almost impossible. FIG. 4 shows a further possibility with which the lateral displacement between the piston end face and the flat 56 can be adjusted.

In the embodiment shown in Figure 4, in which only the support or eccentric ring 252 and one of the pistons 6 are shown, the piston axis 58 always intersects the shaft axis 16, so that the piston axes 58 are each contained in a central plane of the drive shaft 8.

In this exemplary embodiment, the lateral offset is brought about by the fact that the flats (supporting surfaces) are not arranged symmetrically to the central planes through the eccentric axis 20, but offset laterally, so that these central planes divide the flats 256 into two partial surfaces with different widths d, f . This means that the lateral "displacement" of the flattened portion 256 with respect to the piston axis 58 also ensures that the suction control edge 62 just covers the inlet opening 48 in the area of the top dead center of the piston. The exemplary embodiment shown in FIG. 4 is thus a kinematic reversal of the design principle of the exemplary embodiments shown in FIGS. 1 and 3, in which the piston axis, or rather the axis of the inlet opening 48, has been laterally offset with respect to the plane of the shaft axis. In order to achieve the same effect, the flattening 256 is not laterally offset but in the direction of rotation Y (see FIG. 4).

FIGS. 5 and 6 show two further variants in which the end sections of the pistons 6 on the end face have been modified compared to the previously described exemplary embodiments. In the exemplary embodiment shown in FIG. 5, the inlet opening 48 is widened in the mouth region by a chamfer 68, so that the inlet opening 48 is initially opened by the suction control edge 62 to a gap determined by the chamfer 68 at the beginning of the opening process. This variant guarantees a "soft" reversal process from the working stroke to the suction stroke. The introduction of this chamfer in the piston 6 presents no difficulties in terms of production technology, so that this additional variant can be produced very inexpensively.

A particularly good sealing effect between the end face of the piston 6 and the flat 56 can be achieved if a sealing device 70 is provided in the U area of the mouth of the inlet opening 48, by means of which the piston 6 is supported on the flat 56. This can be an elastomeric seal that is biased towards the flat 56 by spring action or by its own elasticity.

By suitably coordinating the flattening width B, the piston diameter, the offset dimension a and the piston stroke (eccentricity e), the suction stroke in the radial piston pump according to the invention can be optimally adapted to the requirements, suction strokes being adjustable over more than 180 ° of a drive shaft revolution .

Claims

claims

1. Radial piston pump with an eccentric (18) drive shaft (8) and with at least one cylinder (4) in which a against a tangential surface (56) of the eccentric (18) biased radial piston (6) is guided, which has a bore has an inlet opening (48) through which fluid can be drawn in from a low-pressure part of the radial piston pump (1), and with a pressure valve (32) assigned to the radial piston (6) in the high-pressure part of the high-pressure pump (1), characterized in that the Relative position of the end face of the radial piston (6) with reference to the tangential surface (56) is selected such that the inlet opening (48) of the bore can be opened by a peripheral edge (62) of the tangential surface (56) located at the back in the direction of rotation (Z) is.

2. Radial piston pump according to claim 1, characterized in that the axis of the inlet opening (48) opposite to the direction of rotation (Z) of the drive shaft (8) offset, at a distance from the vertical plane of the tangential surface (56) containing the central plane of the drive shaft (8) is.

3. Radial piston pump according to claim 1 or 2, characterized in that the axis of the inlet opening (48) lies in a drive shaft center plane and a) (suction control edge of the tangential surface (56) in the direction of the drive shaft rotation direction (Y) offset to the drive shaft. Middle plane is arranged.

Radial piston pump according to one of the preceding claims, characterized in that the inlet opening (48) has a rectangular cross-section, one rectangular edge of which is arranged parallel to the peripheral edge (62) of the tangential surface (56).

5. Radial piston pump according to one of the preceding claims, characterized in that between the eccentric (18) of the drive shaft (8) and the piston (6) on the drive shaft (8) slidably mounted eccentric ring (52) is arranged.

6. Radial piston pump according to claim 5, characterized in that the tangential surface (56) on a radial projection (50) of the eccentric ring (52) is formed.

7. Radial piston pump according to one of the preceding claims, characterized in that the axis of the inlet opening (48) is offset with respect to the piston axis.

8. Radial piston pump according to one of the preceding patent claims, characterized in that a sealing device (70) surrounding the inlet opening (48) is provided in the end face of the radial piston (6) and cooperates with the tangential surface (56).

9. Radial piston pump according to one of the preceding claims, characterized in that the radial piston (6) has an anti-rotation device.

10. Radial piston pump according to one of the preceding claims, characterized in that the inlet opening (48) is widened in the mouth region.

11. Radial piston pump according to one of claims 5 to 10, characterized in that the eccentric ring (52) consists of a material with emergency running properties, preferably bronze.

12. Radial piston pump according to one of the preceding claims, characterized in that the drive shaft (8) three cylinders (4) are assigned.

13. Radial piston pump according to one of the claims 5 to 12, characterized in that the working stroke of the radial piston (6) is limited by a stop in such a way that the eccentric ring (52) cannot tip out of its desired position.